The return-space-escape-backspace configuration is very elegant. Generally the whole layout looks quite natural.
A ton of comments I could make come down to OS background and personal taste. While I love having arrows available to both hands I'd personally want IJKL arrow keys, for example, which better match what I'm used to. But more subtly I'd be concerned about chording to access the arrow keys because I tend to do a lot of multi-chorded arrow strokes already (control-shift-right-right-right) and adding another modifier strikes me as a lot of buttons to juggle at once.
Why not move Tab down to the G? Wouldn't that be an easier location to reach?
Do you find that you still use shift on the opposite hand as what you're shifting, as you need to for a more typical keyboard?